Method for recovering lithium

Abstract

To provide a method for recovering lithium, that is capable of efficiently recovering lithium without containing impurities, such as phosphorus and fluorine, from a lithium-containing solution containing lithium hexafluorophosphate and separated from a lithium ion battery. In the present invention, alkali hydroxide is added to the lithium-containing solution and the solution is made to have pH 9 or more, a precipitate of a phosphate and a fluoride salt is formed, the formed precipitate is separated and removed, and then lithium is recovered from filtrate.

Description

TECHNICAL FIELD[0001]The present invention relates to a method for recovering lithium from a lithium ion battery, and especially relates to a method for recovering lithium, which is capable of preventing contamination by phosphorus and fluorine and recovering lithium of high purity from a lithium-containing solution that contains lithium hexafluorophosphate.BACKGROUND ART[0002]Effective use of electric power is required for recent global warming tendency. Secondary batteries for electric power storage are expected as one means, and from the standpoint of prevention of air pollution, early practical application of large secondary batteries is expected as an automobile power source. Further, a demand of small secondary batteries has been steadily increasing especially in association with spread and performance enhancement of electrical devices, such as digital cameras and mobile phones, as back-up sources of computers and power sources of small household electrical appliances.[0003]As...

AI Technical Summary

Benefits of technology

The present invention helps to efficiently separate and remove a precipitate of phosphate and fluoride salt by adding alkali hydroxide to a solution containing lithium hexafluorophosphate and raising the pH. This allows for the recovery of lithium without contamination by phosphorus and fluorine from the filtrate.

Problems solved by technology

However, in the case of dry treatment like the technology described in Patent Literature 1, consumption of energy and exhaust gas treatment are problems.

Further, especially, in a melting method, lithium is made into slag and becomes unrecoverable, and in a roasting method, contained phosphorus and fluorine are fixed as a water-insoluble phosphate and fluoride.

As a result, separation and refinement become difficult.

Therefore, direct regeneration of lithium, cobalt, and nickel recovered in dry roasting treatment for battery materials is difficult in terms of quality, and effective reuse cannot be achieved.

However, even in such methods using wet treatment, dry treatment is partly used, and realization of low cost is difficult because of complexity of a treatment process.

Therefore, the valuable metals cannot be efficiently recovered.

Especially, regarding lithium of a valuable metal, there is a problem that impurities, such as phosphorus and fluorine, are mixed in, and thus high-quality lithium cannot be efficiently recovered in the form of a simple substance.

This lithium hexafluorophosphate has a hydrolysis reaction through wet treatment, and forms a precipitate in the forms of lithium phosphate (Li3PO4) and lithium fluoride (LiF), and lithium cannot be efficiently recovered in the form of a simple substance.

When separation and refinement treatment is performed in the coexistence of these hydrolysates, ions of these hydrolysates are precipitated on products, resulting in quality failure.

However, the technology described in Patent Literature 2 has problems that phosphorus, fluorine, and lithium are recovered as a coprecipitation mixture, already hydrolyzed phosphate ions cannot be separated, and excessively added fluoride is remained in mother liquor.

However, because behavior of the already hydrolyzed phosphate ions and fluoride ions is different, there is a limit to remove the phosphate ions and the fluoride ions at the same time, and even the technology of Patent Literature 3 cannot sufficiently remove the phosphate and the fluoride.

However, even the technology described in Patent Literature 4 has problems that, in a process of adjusting a solution to have necessary pH for extraction, the hexafluorophosphate ions are hydrolyzed and a precipitate of lithium phosphate and lithium fluoride is generated, becomes crud, and is physically mixed in an extraction solvent, and lithium is contaminated.

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